Systems, methods and devices for acquiring and processing physiological signals

ABSTRACT

A system, method and device are described for biometric analysis using a wearable device. The device can be removeably securable to a user&#39;s skin surface and can include a plurality of electrodes positioned to acquire electrical signals from the skin surface. The device can also include an electromyography acquisition module and skin impedance acquisition module. A processing unit can use the electrodes to capture a plurality of electrical signals including at least one electromyography signal. The processing unit can generate calibration data based on a subset of the captured electrical signals and process the electromyography signals using the calibration data to determine a biometric for the user.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 61/970,454, filed Mar. 26, 2014, U.S. Provisional Patent Application No. 61/970,477, filed Mar. 26, 2014 and U.S. Provisional Patent Application No. 61/970,482, filed Mar. 26, 2014. The entire contents of U.S. Provisional Patent Application No. 61/970,454, No. 61/970,477 and 61/970,482 are hereby incorporated by reference.

FIELD

The various embodiments described herein generally relate to systems, methods and devices for acquiring and processing physiological signals. In particular, the various embodiments described herein use bio-signals acquired from a wearable device for assessing a user's physiological state.

BACKGROUND

Wearable computing systems are an emerging category of devices. These devices enable users to perform a variety of tasks. For example, users may virtually interact with online accounts; record and/or observe information such as videos, images, and sounds; control other computing systems and other connected appliance; interact with other people; and in some instances monitor the current conditions of an individual's body.

Devices capable of monitoring an individual's physical and physiological state have become increasingly popular. Monitoring and maintaining physical fitness is an ongoing concern for individuals with busy lifestyles, and this concern is becoming more pronounced with an aging population. As a result, demand is increasing for devices that can track physical activities and individual fitness.

Many devices currently available provide only minimal insight to users, for example tracking movements using inertial sensors. Devices capable of providing insight into individual physiological responses may improve the utility of such fitness tracking devices by assisting the user to improve aspects of performance, fitness, health and well-being.

SUMMARY OF VARIOUS EMBODIMENTS

In a broad aspect, at least one embodiment described herein provides a biometric analysis system that includes a remote processing device and a wearable device. The wearable device can be removeably securable to a user skin surface with a skin-facing surface of the wearable device positioned to make contact with the skin surface. The wearable device can have a plurality of electrodes positioned to acquire an electrical signal from the skin surface, a controller, a signal acquisition unit operatively coupled to the controller and to the plurality of electrodes, and a wireless communication module operatively coupled to the controller. The signal acquisition unit can include a skin impedance acquisition module and an electromyography acquisition module. The wireless communication module can be used to communicate with the remote processing device. At least one of the controller and the remote processing device can be configured to capture a plurality of electrical signals including at least one electromyography signal using the plurality of electrodes, generate calibration data based on a subset of the plurality of electrical signals, and process the at least one electromyography signal using the calibration data to determine at least one biometric.

In some embodiments, the plurality of electrical signals include at least one skin impedance signal. The subset of electrical signals used to generate the calibration data can include the at least one skin impedance signal.

In some embodiments, the at least one biometric can be at least one of muscle intensity, muscle coordination, muscle ratio, and fatigue. In some embodiments, the wearable device can also include at least one of an inertial measurement unit and a GNSS unit.

In some embodiments, each electrode may be a passive electrode. In some embodiments, each electrode may be an active electrode. In some embodiments, a combination of passive and active electrodes may be used.

In some embodiments, the signal acquisition unit also includes a bio-impedance acquisition module. In some embodiments, the signal acquisition unit also includes a primary multiplexer module. The signal acquisition unit can be coupled to the plurality of electrodes using the primary multiplexer module.

In some embodiments, the signal acquisition unit also includes a primary multiplexer module coupled to the plurality of electrodes and a secondary multiplexer module coupled to the primary multiplexer module. Each of the skin impedance acquisition module and the bio-impedance acquisition module can coupled to the primary multiplexer module by the secondary multiplexer module. The electromyography acquisition module can be coupled directly to the primary multiplexer module.

In some embodiments, the wearable device can also include an analog to digital converter coupled to the controller. Each of the skin impedance acquisition module, the bio-impedance acquisition module, and the electromyography acquisition module can be coupled to the controller by the analog to digital converter. In some embodiments, each of the skin impedance acquisition module, the bio-impedance acquisition module, and the electromyography acquisition module can provide unprocessed signals to the analog to digital converter.

In some embodiments, the electromyography acquisition module can include an amplifier that amplifies the electromyography signal prior to providing the electromyography signal to the analog to digital converter.

In some embodiments, the remote processing device can be a mobile device. The remote processing device can include a display and be configured to display feedback based on the at least one biometric. In some embodiments, the feedback can include at least one of a report on the at least one biometric and a visualization of the at least one biometric.

In some embodiments, the system can also include a cloud server. The cloud server can have a cloud storage module that stores a user profile associated with the wearable device. The user profile can include a historical record of the at least one biometric.

In some embodiments, the system can include a plurality of wearable devices. The cloud storage module can stores a unique user profile for each user in a plurality of users, and each wearable device can be associated with one of the unique user profiles.

In some embodiments, the wearable device can include an alignment guide for aligning the wearable device with a desired region of the skin surface.

In another broad aspect, at least one embodiment described herein provides a wearable device for biometric analysis. The wearable device can have a skin-facing surface that is removeably securable to a user skin surface, with the skin-facing surface positioned to make contact with the skin surface. The wearable device can also include a plurality of electrodes positioned to acquire an electrical signal from the skin surface, a controller, and a signal acquisition unit operatively coupled to the controller and to the plurality of electrodes. The signal acquisition unit can include a skin impedance acquisition module and an electromyography acquisition module. The controller can be configured to capture a plurality of electrical signals including at least one electromyography signal using the plurality of electrodes, generate calibration data based on a subset of the plurality of electrical signals, and process the at least one electromyography signal using the calibration data to determine at least one biometric.

In another broad aspect, at least one embodiment described herein provides a method for biometric analysis using a wearable device positioned to make contact with a skin surface of a user. The wearable device can have a plurality of electrodes positioned to acquire an electrical signal from the skin surface. The method can include capturing a plurality of electrical signals including at least one electromyography signal using the plurality of electrodes and generating calibration data based on a subset of the plurality of electrical signals. The method can also include processing the at least one electromyography signal using the calibration data to determine at least one biometric.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the various embodiments described herein, and to show more clearly how these various embodiments may be carried into effect, reference will be made, by way of example, to the accompanying drawings which show at least one example embodiment, and which are now briefly described.

FIG. 1 is a block diagram illustrating an example embodiment of a system for biometric tracking.

FIG. 2A is a diagram illustrating an exploded view of an example embodiment of a wearable device that can be used in the system of FIG. 1.

FIG. 2B is a diagram illustrating various examples of the placement on a user's body of example embodiments of a wearable device.

FIG. 3 is a block diagram illustrating various components of an example embodiment of a wearable device.

FIG. 4A is a block diagram illustrating various components of an example embodiment of a signal acquisition unit for a wearable device.

FIG. 4B is a block diagram illustrating various components of another example embodiment of a signal acquisition unit for a wearable device.

FIG. 4C is a block diagram illustrating various components of a multiplexer configuration that may be used in an example embodiment of a signal acquisition unit for a wearable device.

FIG. 5 is a flowchart illustrating an example embodiment of the processing that may be performed on acquired bio-signals when using the system of FIG. 1.

FIG. 6 is a flowchart illustrating an example embodiment of a method for biometric analysis.

FIG. 7 is a block diagram illustrating various components used to acquire and process bio-signals in an example embodiment of the biometric tracking system of FIG. 1.

Further aspects and features of the embodiments described herein will appear from the following description taken together with the accompanying drawings.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various systems or methods will be described below to provide an example of an embodiment of the claimed subject matter. No embodiment described below limits any claimed subject matter and any claimed subject matter may cover methods or systems that differ from those described below. The claimed subject matter is not limited to systems or methods having all of the features of any one system or method described below or to features common to multiple or all of the apparatuses or methods described below. It is possible that a system or method described below is not an embodiment that is recited in any claimed subject matter. Any subject matter disclosed in a system or method described below that is not claimed in this document may be the subject matter of another protective instrument, for example, a continuing patent application, and the applicants, inventors or owners do not intend to abandon, disclaim or dedicate to the public any such subject matter by its disclosure in this document.

Furthermore, it will be appreciated that for simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. Also, the description is not to be considered as limiting the scope of the embodiments described herein.

It should also be noted that the terms “coupled” or “coupling” as used herein can have several different meanings depending in the context in which these terms are used. For example, the terms coupled or coupling can have a mechanical, electrical or communicative connotation. For example, as used herein, the terms coupled or coupling can indicate that two elements or devices can be directly connected to one another or connected to one another through one or more intermediate elements or devices via an electrical element, electrical signal or a mechanical element depending on the particular context. Furthermore, the term “communicative coupling” may be used to indicate that an element or device can electrically, optically, or wirelessly send data to another element or device as well as receive data from another element or device.

It should also be noted that, as used herein, the wording “and/or” is intended to represent an inclusive-or. That is, “X and/or Y” is intended to mean X or Y or both, for example. As a further example, “X, Y, and/or Z” is intended to mean X or Y or Z or any combination thereof.

It should be noted that terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree may also be construed as including a deviation of the modified term if this deviation would not negate the meaning of the term it modifies.

Furthermore, any recitation of numerical ranges by endpoints herein includes all numbers and fractions subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.90, 4, and 5). It is also to be understood that all numbers and fractions thereof are presumed to be modified by the term “about” which means a variation of up to a certain amount of the number to which reference is being made if the end result is not significantly changed.

Described herein are example embodiments of systems, methods and wearable devices for determining various biometric features for an individual user. Generally, the various biometric features can be determined by capturing a plurality of electrical signals from a skin surface of the user, including at least one electromyography signal. Calibration data can be generated based on a subset of the captured electrical signals, and the electromyography signals can be processed using the calibration data to determine at least one biometric. Examples of biometric features that may be determined in various embodiments described herein include muscle intensity, muscle coordination, muscle ratio, muscle fatigue, lactate levels, and hydration.

The example embodiments of the systems and methods described herein may be implemented as a combination of hardware or software. In some cases, the example embodiments described herein may be implemented, at least in part, by using one or more computer programs, executing on one or more programmable devices comprising at least one processing element, and a data storage element (including volatile and non-volatile memory and/or storage elements). These devices may also have at least one input device (e.g. a pushbutton keyboard, mouse, a touchscreen, and the like), and at least one output device (e.g. a display screen, a printer, a wireless radio, and the like) depending on the nature of the device.

It should also be noted that there may be some elements that are used to implement at least part of one of the embodiments described herein that may be implemented via software that is written in a high-level computer programming language such as object oriented programming. Accordingly, the program code may be written in C, C⁺⁺ or any other suitable programming language and may comprise modules or classes, as is known to those skilled in object oriented programming. Alternatively, or in addition thereto, some of these elements implemented via software may be written in assembly language, machine language or firmware as needed. In either case, the language may be a compiled or interpreted language.

At least some of these software programs may be stored on a storage media (e.g. a computer readable medium such as, but not limited to, ROM, magnetic disk, optical disc) or a device that is readable by a general or special purpose programmable device. The software program code, when read by the programmable device, configures the programmable device to operate in a new, specific and predefined manner in order to perform at least one of the methods described herein.

Furthermore, at least some of the programs associated with the systems and methods of the embodiments described herein may be capable of being distributed in a computer program product comprising a computer readable medium that bears computer usable instructions for one or more processors. The medium may be provided in various forms, including non-transitory forms such as, but not limited to, one or more diskettes, compact disks, tapes, chips, and magnetic and electronic storage. In alternative embodiments, the medium may be transitory in nature such as, but not limited to, wire-line transmissions, satellite transmissions, internet transmissions (e.g. downloads), media, digital and analog signals, and the like. The computer useable instructions may also be in various formats, including compiled and non-compiled code.

Electromyography (EMG) measures electromyographic signals, which are electrical signals associated with muscle contractions. There are generally two methods for acquiring EMG signals. The first method may be referred to as needle electromyography, and is an invasive method that involves inserting electrical probes (needles) into target muscle tissues in order to acquire the EMG signal from the muscle. While needle electromyography has been used to measure and analyze muscle contractions and activity; this application has typically been limited to hospital or laboratory settings.

The second method is referred to as surface electromyography (sEMG) and involves placing sensors at the skin surface close to target muscles. While less invasive than needle EMG, sEMG has much lower specificity than needle EMG. Surface EMG signals result from the superposition of the sensed motor unit action potentials (MUAPs) from all the muscle fibers within sensing distance of the acquiring electrode. The MUAPs seen in the sEMG signal may be generated by the same muscle or may originate in different muscles. This can result in signal cross-talk where the sEMG energy from one particular muscle is sensed at an electrode location for a different muscle.

Acquired sEMG signals may also contain other undesirable components that are sensed along with the desired muscle activity. For instance, the undesirable components may include environmental noise (e.g. 60 Hz power line “hum”) and/or body-produced signals such as electrical signals from the heart (electrocardiograph (ECG) signals).

Surface EMG may also be susceptible to “motion artifact” noise which results from the relative motion of the sEMG electrode and the muscle tissue. Motion artifact noise can result from muscle fibres moving underneath the surface of the skin relative to a fixed sensor position during a dynamic contraction (e.g. Bicep curl). This type of motion artifact is independent of the sensor used because the muscle always moves underneath the skin.

Motion artifacts may also occur where electrodes are positioned at the surface of the skin and can shift position relative to the muscles being targeted due to the skin's pliability. The “motion artifact” effect may be more pronounced when using electrodes embedded in a wearable device (such as textile electrodes or conductive polymers) as compared with sensors adhered to the surface of the skin. This may affect the signal contribution from target muscles as well as undesirable signal components acquired from nearby non-targeted muscles. In some cases, the “motion artifact” noise may appear as a low frequency component of the desired sEMG signal, while in other cases it may partially overlap signal components that include the desired frequency content of the sEMG signal. Examples of signal processing methods described in accordance with the teachings herein can be applied to remove the unwanted interference from acquired sEMG signals. Using compressive garments may also mitigate some of the motion artifact noise by reducing the motion of the electrodes in the garment relative to the targeted muscles.

Wearable devices and systems incorporating wearable devices have recently been developed for a variety of purposes. Wearable devices can be used for controlling and interacting with multimedia and other electronic devices, as well as for fitness and athletic applications. Described herein are example embodiments of wearable devices, systems incorporating one or more wearable devices, and methods for biometric analysis. The systems, methods and devices described herein can be applied for fitness and athletic applications such as monitoring and analyzing performance, and avoiding injury.

The systems, methods and devices described herein can acquire a plurality of electrical signals, including sEMG signals, and analyze those signals to provide physiological insights to users. In addition to EMG signals, other electrical signals such as skin impedance signals and bio-impedance signals may be acquired, as well as signals from other sensors such as location and motion sensors. A user's biometric features, as well as other metrics, may be monitored and stored during physical activity and at other times. The biometric features and other metrics may be provided as real-time feedback to a user and/or tracked over time to monitor and illustrate a user's progress.

A user's body impedance provides a measure of how well the user's body impedes the flow of electric current. A user's body impedance can be separated into the impedance of the user skin surface, referred to as skin impedance, and the impedance of the user's body below the skin surface, referred to as bio-impedance. EMG signals acquired from a user's skin surface will be affected by the skin impedance.

A user's skin impedance generally depends on the condition of the surface of the user's skin. As a result, the user's skin impedance can change as the user performs an activity, for example when the user perspires. In general, a user's skin impedance will be lower when the skin surface is wet than when the skin surface is dry.

Bio-impedance can be affected by a user's body composition, as different tissue types tend to have different levels of resistivity. For example, fat tissue has high resistivity, while tissues with high water content will tend to have low resistivity. A user's bio-impedance can also fluctuate as the user performs an activity, for example due to changes in the user's hydration level, which can affect the user's intra-cellular and extra-cellular water content.

The various biometric features and metrics determined for a user may be analyzed to identify trends and alert users to those trends. This may enable users to adjust the activities they are performing, or how they are performing activities in response to the trends. For instance, the signal amplitude and frequency content of acquired EMG signals may be analyzed over time to identify muscle growth or muscle efficiency trends. Similarly, muscle coordination (the sequence in which an individual's muscles are operating) may be analyzed to provide recommendations to improve individual performance. Muscle balance (cross-body) may be tracked and recommendations may be provided to users to adjust their training if muscles appear to be unbalanced. The various biometric features and metrics may also be analyzed to identify an injury risk trend, provide feedback to a user indicating a potential risk of injury, and provide recommendations to avoid the potential risk of injury.

Muscle fatigue may be tracked and a fatigue alert may be provided to the user when a fatigue trend is identified. A fatigue alert may be used to prevent overtraining. In some embodiments, fatigue may be determined by measuring decreases in mean and median frequencies of EMG signals. For example, this may be done using machine learning algorithms pre-trained on a plurality of collected EMG signals.

Similarly, hydration may be tracked to provide feedback to a user to drink water or other fluids when their body exhibits signs of low hydration. Lactate levels may also be monitored to provide feedback to a user, and may provide a recommendation of reducing activity intensity when lactate levels are identified above a particular threshold.

Referring now to FIG. 1, shown therein is block diagram illustrating an example embodiment of a system 100 for biometric analysis. System 100 includes a wearable device 102, one or more remote processing devices 108 and a remote cloud server 110. In other embodiments, systems for biometric analysis in accordance with the teachings herein may not require any remote processing devices 108 or remote cloud server 110. In such embodiments, the processing of the bio-signals acquired from a user may be performed by electronic components included in wearable device 102.

Wearable device 102 can be removeably securable to a user skin surface with a skin-facing surface of the wearable device positioned to make contact with the skin surface. Wearable device 102 can generally be manufactured of a fabric, cloth or polymer material suitable for being worn in contact with a user's skin. A portion, or all, of the wearable device 102 can be made of breathable materials to increase comfort while a user is performing an activity.

In some embodiments, the wearable device 102 may be formed into a garment or form of apparel such as a band, shirts, shorts, and sleeves for example. In some cases, wearable device 102 may be a compression garment manufactured from a material that is compressive. A compression garment may minimize the impact from “motion artifacts” by reducing the relative movement of the wearable device 102 with respect to a target muscle. In some cases, wearable device 102 may also include anti-slip components on the skin-facing surface. For example, a silicone grip may be provided on the skin-facing surface of the wearable device 102 to further reduce the potential for motion artifacts. In some cases, the weave of a compression garment textile can be optimized to minimize motion artifacts by reducing motion in preferred directions of the textile weave. For example, additional compression (in addition to the compression elsewhere in the garment) can be added to a compression garment in locations having electrodes.

Wearable device 102 includes a plurality of electrodes 106 a-106 n positioned to acquire an electrical signal from the user's skin surface. In some embodiments, the electrodes 106 can be integrated into the material of the wearable device 102. Alternatively, the electrodes 106 can be affixed or attached to the wearable device 102, e.g., printed, glued, laminated or ironed onto the skin-facing surface. In some cases, the electrodes 106 may be provided separately from the wearable device 102 as an iron-on component that a user can then apply to the wearable device 102. Various other methods of affixing the electrodes 106 to the wearable device 102 may also be used.

Various different electrodes 106 may be used with wearable device 102. For example, the electrodes 106 may be metallic, conductive polymers, conductive inks, or conductive textiles for example.

Wearable device 102 also includes an electronics module 104 coupled to the plurality of electrodes 106. Generally, the electronics module 104 can include a power supply, a controller, a memory, a signal acquisition unit operatively coupled to the controller and to the plurality of electrodes 106, and a wireless communication module operatively coupled to the controller. The signal acquisition unit may include a skin impedance acquisition module and an electromyography acquisition module. In some cases, the signal acquisition unit may also include a bio-impedance acquisition module and/or an analog-to-digital converter. Example embodiments of the wearable device 102 will be described in further detail below, with reference to FIGS. 2 to 4.

The electronics module 104 of the wearable device 102 can be communicatively coupled to one or more remote processing devices 108 a-108 n, e.g., using a wireless communication module (e.g., Bluetooth, IEEE 802.11, etc.). The remote processing devices 108 can be any type of processing device such as a personal computer, a tablet, and a mobile device such as a smartphone or a smartwatch for example. The electronics modules 104 can also be communicatively coupled to the cloud server 110 over, for example, a wide area network such as the Internet.

Each remote processing device 108 and remote cloud server 110 can include a processing unit, a display, a user interface, an interface unit for communicating with other devices, Input/Output (I/O) hardware, a wireless unit (e.g. a radio that communicates using CDMA, GSM, GPRS or Bluetooth protocol according to standards such as IEEE 802.11a, 802.11b, 802.11g, or 802.11n), a power unit and a memory unit. The memory unit can include RAM, ROM, one or more hard drives, one or more flash drives or some other suitable data storage elements such as disk drives, etc.

The processing unit controls the operation of the remote processing device 108 or the remote cloud server 110 and can be any suitable processor, controller or digital signal processor that can provide sufficient processing power processor depending on the desired configuration, purposes and requirements of the system 100.

The display can be any suitable display that provides visual information. For instance, the display can be a cathode ray tube, a flat-screen monitor and the like if the remote processing device 108 or remote cloud server 110 is a desktop computer. In other cases, the display can be a display suitable for a laptop, tablet or handheld device such as an LCD-based display and the like.

System 100 can generally be used for tracking biometric features and other metrics for a user. For example, the biometric features and other metrics may be monitored, stored, and analyzed for the user. In different embodiments, aspects of the monitoring, storage and analysis of the different biometric features and other metrics may be performed by the wearable device 102, a remote processing device 108, or the cloud server 110.

The cloud server 110 may provide additional processing resources not available on the wearable device 102 or the remote processing device 108. For example, some aspects of processing the signals acquired by the electrodes 106 may be delegated to the cloud server 110 to conserve power resources on the wearable device 102 or remote processing device 108. In some cases, the cloud server 110, wearable device 102 and remote processing device 108 may communicate in real-time to provide timely feedback to a user regarding their current biometrics and any trends identified.

For example, one of the controller (on the wearable device 102) and the remote processing device 108 can be configured to capture a plurality of electrical signals including at least one electromyography signal using the plurality of electrodes 106. The controller or the remote processing device 108 can generate calibration data based on a subset of the plurality of electrical signals acquired. The at least one electromyography signal can then be processed using the calibration data to determine at least one biometric.

In some embodiments, the acquired electrical signals may include at least one skin impedance signal. The controller or the remote processing device 108 can generate the calibration data based on a subset of the electrical signals that includes the at least one skin impedance signal. Thus, the calibration data may be used to adjust the processing of the acquired electromyography signals to account for changes in skin impedance.

As the acquired sEMG signals may be variable depending on skin condition, calibrating the processing to respond to changes in skin impedance may account for changes in skin condition that affect the raw EMG signal acquired. For example, as a user begins to perspire, moisture accumulates on the skin surface, changing the skin's effective impedance. This can affect the acquired EMG signal, or it may be used as an indication of exertion. Therefore a “skin impedance signal” can be acquired and used to identify the skin impedance.

The skin impedance signal is a form of electrical signal that can be acquired by injecting a probe signal at a first electrode and receiving a resulting signal at a second electrode. Generally, skin impedance signals are injected and received through neighboring or proximate electrodes, to maximize the effect of skin impedance. The skin impedance signal can be analyzed periodically or continuously to account for the changes in the acquired EMG signal due to perspiration.

In some embodiments, bio-impedance signals may also be acquired by wearable device 102. Bio-impedance signals are another form of body impedance, which can be affected by changes in a user's hydration levels, among other factors. Dehydration can cause an increase in the body's electrical resistance, and the bio-impedance signals can be used to analyze an individual's hydration levels.

The bio-impedance signal is a form of electrical signal that can be acquired using a tetra-polar electrode configuration. A probe signal can be injected using a first pair of electrodes and a resulting signal can be received at a second pair of electrodes. The bio-impedance signal can be analyzed periodically or continuously to determine biometrics for the user such as changes in hydration levels. In some cases, bio-impedance signals may be injected and received through cross-body or otherwise distant electrode pairs. This may provide a broader view of the state of the user's body, as compared with a localized view that may be provided if the electrode pairs are close together. Accordingly, using cross-body or otherwise distant electrodes may improve the accuracy of the hydration analysis.

EMG signals can be collected using a differential pair of electrodes. That is, two electrodes can be used to acquire a differential signal for a single EMG acquisition channel. Typically, EMG signal collection can be paused while skin impedance signals and/or bio-impedance signals are acquired. The signal injection used to measure the skin impedance or bio-impedance may saturate the analog front end components of the EMG acquisition unit. Accordingly, the EMG signal collection can be paused while skin impedance or bio-impedance signals are acquired to avoid interference.

In some cases, a single set of electrodes can be used to acquire skin impedance signals, bio-impedance signals, and EMG signals. In such cases, the signal acquisition unit may include multiplexers (or switching networks) that can be used to switch between the skin impedance acquisition unit, bio-impedance acquisition unit and EMG acquisition unit. Example embodiments of signal acquisition units employing multiplexers will be discussed in further detail below with reference to FIGS. 4A to 4C.

In some embodiments, system 100 may include a plurality of wearable devices 102 that can be removeably secured to the user's skin surface. In some cases, each of the wearable devices 102 may communicate with each other or with remote processing device 108 or cloud server 110. Using a plurality of wearable devices 102 may better facilitate cross-body or contralateral comparisons of EMG signals and other acquired signals. This may facilitate additional biometric features to be determined from the acquired signals.

In some cases, prior to using a wearable device 102 a user may populate a user profile. The user profile may include user demographic data such as sex, height, weight, age, and other demographic details. In some embodiments, a user's demographic data may affect the processing used to determine biometric features or other metrics for that user. For example, determined calorie expenditure may be affected by a user's height and weight, while lactate levels may be affected by a user's sex.

The user profile may also track the various biometric features and other metrics determined for a user over time. Accordingly, a user's profile may include a historical record of one or more biometrics or other metrics for that user.

The user profile may be stored in various locations. For example, in some embodiments a user's profile can be stored in a memory module of the wearable device 102 or in a remote processing device 108. A user's profile may also be stored in a cloud storage module on cloud server 110 in some embodiments. Where user profiles are stored in multiple locations, the various components may communicate to update features of the user's profile.

In some cases, different aspects of a user's profile may be stored in different locations due to storage limitations. For example, the wearable device 102 or remote processing device 108 may store limited portions of a user's profile necessary for determining biometric features and other metrics. Additional portions of the user's profile could then be stored on the remote cloud server 110 for retrieval by (and syncing with) wearable device 102 and remote processing device 108.

In some cases, baseline initialization data may be generated for a user when they first use a wearable device 102. For example, the wearable device 102 or remote processing device 108 may indicate to the user basic activities to perform in an initialization routine. The initialization routine may include the individual performing activities that result in a maximum voluntary contraction (MVC) of target muscles with the wearable device 102 positioned to collect EMG signals from those muscles. The user may be instructed to perform particular activities with maximum strength, and the acquired EMG signals can be used as a reference for analysis of subsequently acquired signals. In some cases, muscle strength/power may be initialized through a standard cycling power meter and stored in the user profile for future reference.

The initialization process can be repeated for different target muscles and used to generate baseline physiological data. In some cases, some baseline physiological data may be provided with the wearable device 102 without requiring the user to perform a calibration routine. This baseline physiological data may be pre-generated based on aggregate calibration data from a number of other users. The baseline physiological data also may be adjusted based on demographic data provided in the user's profile. Baseline physiological data can be stored in the user's profile and used to identify changes or trends in the user's physiological state or physiological responses. In some cases, the baseline physiological data may be updated over time to account for changes in the user's physiology, as detected by system 100.

In some cases, the remote cloud server 110 may store a unique user profile for each user in a plurality of users. Each unique user profile may be associated with one or more wearable devices 102 used by the corresponding user. In some cases, the unique user profile may be associated with a particular remote processing 108 used by a user. The remote cloud server 110 may provide an interactive community for various users of the wearable devices 102 to compare biometric features and other features determined by wearable devices 102.

The remote cloud server 110 may also enable longer term trends or patterns to be identified for a user or a collective of users. For example, remote cloud server 110 may analyze biometric data acquired from a particular user over a period of time (e.g., several days, weeks, months or even years) to identify a pattern indicative of potential injury or existing injuries. The remote cloud server 110 may then provide an alert to remote processing device 108 or wearable device 102 associated with that user alerting them to the identified trend. Monitoring and tracking various biometrics and metrics for a user over time can also be used to monitor rehabilitation progress and/or to monitor performance improvements over time. For example, trends can be used to ascertain training goals leading up to a set date, such as a competition date. This trend data can be used to facilitate the athlete “peaking” at the competition date.

Referring now to FIG. 2A, shown therein is an exploded view of an example embodiment of a wearable device 200, which may be an embodiment of wearable device 102. Wearable device 200 is an example of a band-type wearable device that can be worn at various positions on a user's body, as shown in FIG. 2B.

As shown, wearable device 200 is manufactured of an elastic or compressive material, such as neoprene, elastane or the like, with a plurality of electrodes interwoven into the material 202 of the wearable device. For example, the electrodes may be manufactured of conductive fabrics, to maintain the flexibility of wearable device 200. In one example embodiment, the material 202 may be an elastane polyester blend and the electrodes may be manufactured of conductive nylon.

However, in other embodiments, wearable device 200 may be manufactured of non-compressive material, or without interwoven electrodes. For example, electrodes may be fastened on the interior surface of wearable device 200 using a suitable adhesive, stitching or other fastener. In some cases, the electrodes can be secured in wearable device 200 by overmolding.

The electrodes may be located in specific regions of the wearable device 200 so as to be positioned proximate to target muscles. For example, where wearable device 200 is a thigh band, a set of electrodes may be positioned to overlie the vastus lateralis (VL) muscle of the quadriceps. In some cases, another set of electrodes may be positioned to overlie muscles of the hamstring. In other embodiments where wearable device 200 is intended to be worn over another limb, or another portion of a limb, electrodes may be positioned differently to overlie muscles of interest. In some cases, the electrodes can be configured to acquire an aggregate signal from a group of targeted muscles.

To ensure that a user has the wearable device 200 in a proper position for the embedded electrodes, wearable device 200 may also include an alignment guide to indicate the optimal orientation of the wearable device 200 when being worn. In some cases, the electrical signals received using the electrodes in the wearable device 200 may be compared to stored alignment data. Based on this comparison, an alert may be provided to the user to adjust the wearable device 200 for optimal sensor placement. In some cases, the stored alignment data may be dependent on the particular activity being performed by the user.

For example, the acquired electrical signals can be monitored for an expected sequence of muscle activations for a known movement associated with the activity. The acquired electrical signals can be compared with stored alignment data to identify any discrepancies in a received muscle coordination pattern. Based on the detection of a discrepancy, it can be determined that the sensors are not located in the optimal locations. In some cases, the amplitude of the acquired electrical signals can be analyzed. If the amplitude is below a predetermined amplitude threshold, it can be determined that the sensors are not proximal to the target muscle(s). In some cases, the frequency content of the received electrical signals can be analyzed to determine if motion artifact signal components are outside expected values. If so, this may indicate that the wearable device 200 is not being worn correctly.

In some cases, the alignment data can be generated by a user performing a baseline initialization routine. For example, the system 100 (e.g. wearable device 102 or remote processing device 108) may indicate to the user a sequence of actions that require the user to contract one or more muscles in a particular manner. The electrical signals acquired while the user performs the sequence of actions can be used to generate the alignment data. The alignment data can then be stored in the user profile on the wearable device 102, remote processing device 108 or remote cloud server 110. In some cases, the predetermined amplitude threshold can be determined based on the electrical signals acquired during the training routine and be stored as part of the alignment data.

In some cases, the plurality of electrodes in the wearable device 200 may include a greater number of electrodes than needed. This can be done to provide an even distribution of electrodes throughout the wearable device 200 to minimize the potential for misalignment. In such cases, the signals received from the plurality of electrodes can be compared with stored alignment data, and a subset of electrodes having desired signal components can be identified for use, based on the comparison.

Conductive wires 206 are coupled to the electrodes to convey the acquired signals to circuit board 204. In some cases, the conductive wires 206 may be conductive textile threads. The conductive wires 206 may be gold-plated to improve conductivity. Circuit board 204 contains the various electronic components of wearable device 200 such as a signal acquisition unit and controller. Electronic components of wearable device 200 will be described in further detail below with regard to FIGS. 3 and 4.

The wearable device 200 also includes a battery 208 to power the circuit board 204. In some cases, one or more user inputs 210 may be provided to allow a user to activate/deactivate the wearable device 200 or adjust parameters of the wearable device. For example, the user input 210 may be a push button or capacitive sensor that can be used to activate the wearable device 200.

One or more status indicators, such as light emitting diodes (LEDs), or a display, may be provided on outer cover 220 to indicate the status of wearable device 200 to the user. In some cases, a display integrated into outer cover 220 may also provide additional feedback to a user that may include biometrics or other metrics determined according to the teachings described herein. The wearable device 200 may also include haptic feedback modules to provide haptic feedback to a user regarding the status of the wearable device 200 or alerts regarding the biometrics or other metrics determined for that user.

The various electronic components of the wearable device 200 can be contained within a waterproof casing. The waterproof casing can be provided by water-tight casing 216, outer cover 220 and an O-ring 218 between the water-tight casing 216 and the outer cover 220. The waterproof casing can prevent malfunctioning of the electronic components of the wearable device 200 by preventing liquids such as sweat or rain water from coming into contact with the circuit board 204. This may also allow the wearable device 200 to be cleaned after use to improve hygiene. In some cases, the electronic components in the water-tight casing can be removed from wearable device 200 to ensure that they are not damaged when wearable device 200 is cleaned.

Wearable device 200 may also include an electronics module seat 214. The seat 214 can be used to join the electronic components of the wearable device to the materials to be worn on the user's skin surface. The seat 214 may be a rubberized ring to minimize the rigidity felt by a user. This may minimize the discomfort felt by a user, and reduce potential interference with normal range of motion. In some cases, the electronic components of the wearable device may be environmentally sealed and joined to the material 202 of the wearable device 200 using an overmold process. This may also provide a waterproof casing for the electronic components of wearable device 200.

Referring now to FIG. 2B, shown therein is a diagram 250 illustrating some examples of locations where a wearable device 260, such as wearable device 200, may be removeably secured to a user's skin surface. In the example shown in FIG. 2B, wearable devices 260 are shown attached to the user skin surface at the upper arm, lower arm, waist, thigh and lower leg. A skilled person will appreciate that other suitable placements may also be selected for a wearable device 260.

In some cases, the particular placement of a wearable device 260 may be determined based on a particular activity being undertaken by an individual. In some cases, an individual may select a particular placement based on nearby muscle groups the individual wishes to track. For example, a user may select the thigh or lower leg when targeting different muscles in the legs, and the lower or upper arm when performing activities that target the muscles of the arms.

In some cases, an individual may select a particular placement for a wearable device 260 because it is close to or distant from large muscle groups. For example, a user may select a hip bone as a placement for a wearable device as that region does not have high intensity muscle activity in its immediate vicinity. In some cases, one or more electrodes in a wearable device 260 may be used as reference electrodes that are not intended to capture EMG signals. For example, a reference electrode may be placed on the user's hip bone, at a location distant from most muscle activity, thereby minimizing the contribution of EMG signals to the electrical signals acquired by the reference electrode.

In some cases, the particular placement of a wearable device 260 may be dependent on the size or shape of that particular wearable device. For example, a wearable device 260 that can be placed around a user's waist may be different from a wearable device 260 that can be placed around a user's calf or forearm.

Referring now to FIG. 3, shown therein is a block diagram of an example embodiment of a wearable device 300. Wearable device 300 is an example embodiment of a wearable device 102, 200 or 260 that can be used in biometric tracking system 100. In various embodiments, wearable device 300 can include additional components not shown in FIG. 3, such as a battery module, an input module or user interface.

Wearable device 300 includes a plurality of electrodes 306A-306N. The plurality of electrodes 306 are positioned in wearable device 300 to acquire an electrical signal from a user's skin surface when wearable device 300 is secured to the user's skin surface. For example, the electrodes 306 may be exposed on the skin-facing side of the wearable device 300 such that they are in contact with the user skin surface when the wearable device 300 is secured to the user skin surface. In some embodiments, some or all of the electrodes 306 may be capacitively coupled to the user skin surface, in which case they may not make electrical contact with the skin surface (e.g., due to an insulating coating).

In some embodiments, the electrodes 306 may be passive electrodes. In other embodiments, some or all of the electrodes 306 may be active sensors or electrodes, which contain active electronics that may require power to operate. Examples of active electronics include front-end amplifiers or filters. Given the low signal-to-noise ratio (SNR) often found with sEMG signals, active sensors may be used to increase front-end gain and reject common-mode noise. This can increase SNR of the acquired electrical signals before further processing.

Passive electrodes may be preferred in some applications due to the low-energy associated with their use. This can prolong the battery life of wearable device 300 thereby improving its utility for tracking a user's activity over prolonged periods. Passive electrodes may also be more easily integrated in garments.

In some embodiments, wearable device 300 can incorporate a compression garment or compressible garment. A compression garment can be used to reduce the relative movement between the location of the electrodes 306 and muscles being targeted. This can minimize the effect of motion artifacts on the EMG signals acquired.

Wearable device 300 also includes signal acquisition unit 302. Signal acquisition unit 302 can be used to receive and process, or pre-process, the signals acquired using electrodes 306.

Signal acquisition unit 302 can include an EMG acquisition module 310, a skin impedance acquisition module 312, a bio-impedance acquisition module 314 and an analog-to-digital converter 316 (A/D converter). In some embodiments, analog-to-digital converter 316 can be implemented using a high resolution, high dynamic range A/D converter. For example, the analog-to-digital converter 316 may sample the electrical signals acquired by electrodes 306 at, for example, 500 to 8000 samples per second and convert the signals to discrete time series data signals.

In some cases, one or more of EMG acquisition module 310, skin impedance acquisition module 312, bio-impedance acquisition module 314 may amplify the analog signal (to increase SNR) before providing the analog signal to ND 316. In some cases, EMG acquisition module 310, skin impedance acquisition module 312, bio-impedance acquisition module 314 may provide unfiltered signals to analog-to-digital converter 316. Example embodiments of signal acquisition unit 302 will be described in further detail below with reference to FIG. 4.

Signal acquisition unit 302 may be configured to acquire a plurality of analog electrical signals using the plurality of electrodes 306 and to convert the acquired electrical signals in unfiltered form to digital signals using analog-to-digital converter 316. For example, A/D converter 316 may sample a continuous time analog EMG signal or other electrical signal and convert them to discrete time samples digital signals. This may provide a high quality digital signal with high levels of both undesirable signal components (e.g., noise) and EMG signals of interest (or skin impedance signal or bio-impedance signals). Various digital signal processing techniques can then be used to extract the desired signal components for analysis in determining biometric features and other metrics.

In some embodiments, signal acquisition unit 302 may not require A/D converter 316. For example, where controller 304 has a built-in A/D converter, A/D converter 316 may not be necessary. In such cases, the EMG acquisition module 310, skin impedance acquisition module 312, and bio-impedance acquisition module 314 may be coupled directly to controller 304.

Signal acquisition unit 302 is operatively coupled to controller 304. Controller 304 can be configured to control the signal acquisition unit 302 and to acquire a plurality of electrical signals using the plurality of electrodes 306. In some embodiments, controller 304 may also be configured to process the acquired electrical signals to determine at least one biometric feature or other metric. Controller 304 may be, for example, a microcontroller or a microprocessor, such as an ARM-based processor.

Controller 304 may be operatively coupled to memory module 318. In some cases, memory module 318 may include volatile and/or non-volatile memory. Non-volatile memory can be used to store program data, such as executable instructions, and signal data such as raw and/or processed electrical signal data (e.g. EMG data, skin impedance data, bio-impedance data), additional sensor data, calibration data, and operational parameters for example. Similarly, volatile memory may be used to store program data and signal data on a temporary basis.

Controller 304 may also be operatively coupled to a communication module 308. Communication module 308 may be a wireless communication module used to communication with remote processing device 108 or cloud server 110. In some cases, controller 304 may communicate the unprocessed digital signals received from analog-to-digital converter 316 to remote processing device 108 for further processing. For example, communication module 308 may communicate with remote processing device 108 using various communication protocols such as Bluetooth™ Low-Energy (BTLE), ANT+ or IEEE 802.11 (WiFi™).

Communication module 308 may also include other interfaces for communicating with remote processing devices 108 and cloud server 110. For example, communication module 308 may include ports for wired connections such as a Universal Serial Bus (USB) or other port. In some cases, wearable device may also include removable storage modules such as an SD card for transferring acquired data to a remote processing device 108.

Controller 304 can operate as an interface between the signal acquisition unit and the processing of the acquired signals. In some cases, controller 304 may process the acquired signals itself in real-time or near real-time. In some cases, controller 304 may store the unprocessed signals or transmit processed or unprocessed signals to a remote processing device 108 or cloud server 110 for analysis using communication module 308.

Controller 304 may be coupled to additional sensor module 320. Additional sensor module 320 may include one or more additional sensors used to acquire data regarding an activity being undertaken in addition to the electrical signals acquired from the user skin surface. In wearable device 300 as shown, the additional sensor module 320 includes an inertial measurement unit (IMU) 322 and a Global Navigation Satellite System (GNSS) unit 324, however other sensors may also be used.

IMU 322 can include one or more sensors for measuring the position and/or motion of the wearable device. For example, IMU 322 may include sensors such as a gyroscope, accelerometer (e.g., a three-axis accelerometer), magnetometer, orientation sensors (for measuring orientation and/or changes in orientation), angular velocity sensors, or inclination sensors.

GNSS unit 324 can include one or more sensors or devices used to determine the GNSS coordinates of the wearable device using one or more GNSS system, such as the Global Positioning System (GPS), Galileo, GLONASS, or the like. GNSS coordinates can be used to track a user's movement or determine location, and supplement the analysis performed by controller 304. GNSS coordinates can also be provided to cloud server 110 to facilitate comparisons or communication with other users in close proximity. GNSS coordinates can also be used to determine various metrics related to the user activity, such as weather and other atmospheric information.

Wearable device 300 may also include an output module 330 coupled to controller 304. Output module 330 may include one or more output or feedback devices that can provide a user of wearable device 300 with information regarding the status of wearable device 300 as well as feedback on the user's biometrics and other metrics. For example, output module 330 may include one or more status indicators such as an LED, light, or a haptic feedback module. Output module 330 may also include a display such as an OLED or LSC display for providing feedback and indications of status to the user.

Referring now to FIG. 4A, shown therein is a block diagram 400 illustrating components in an example embodiment of a signal acquisition sub-unit 402, which may be used in an embodiment of signal acquisition unit 302.

Signal acquisition sub-unit 402 illustrates how multiplexers can be used to allow skin impedance signals, bio-impedance signals, and EMG signals to be acquired using the same electrodes. In some cases, a signal acquisition unit may include two signal acquisition sub-units such as signal acquisition sub-unit 402, each coupled to a separate electrode pair. In some cases, each signal acquisition sub-unit may have a separate A/D converter, while in other embodiments a single A/D converter can be used to convert the electrical signals acquired by each signal acquisition sub-unit. Another example embodiment of a signal acquisition unit employing multiplexers will be described with reference to FIG. 4B.

Signal acquisition sub-unit 402 is coupled to an electrode pair 406 and a controller 404. As shown in block diagram 400, the signal acquisition unit 402 includes a primary multiplexer 420 and the signal acquisition unit 402 is coupled to electrode pair 406 by primary multiplexer 430. Signal acquisition sub-unit 402 also includes EMG acquisition module 410, skin impedance acquisition module 412, bio-impedance acquisition module 414 and A/D converter 416. The EMG acquisition module 410 is coupled directly to the primary multiplexer 430.

Signal acquisition sub-unit 402 further includes a secondary multiplexer 432. Each of the skin impedance acquisition module 412 and the bio-impedance acquisition module 414 is coupled to the primary multiplexer 430 by the secondary multiplexer 432. The primary multiplexer 430 and secondary multiplexer 432 can be used to switch the acquisition units that are currently sampling the electrodes of electrode pair 406. This can enable the same electrodes to be used by the EMG acquisition module 410, skin impedance acquisition module 412, and bio-impedance acquisition module 414.

Referring now to FIG. 4B, shown therein is block diagram 450 showing components in an example embodiment of a signal acquisition unit 452, which may be an embodiment of signal acquisition unit 302. In the example shown in block diagram 450, signal acquisition unit 452 is coupled to 4 electrodes 406A, 406B, 406C and 406D. When a wearable device is secured to a user skin surface, the electrodes 406 can be positioned to acquire electrical signals from the skin surface.

As shown in block diagram 450, the electrodes may be configured as a first electrode pair 406A and 406B, and a second electrode pair 406C and 406D. Each electrode pair is coupled to a primary switch network 480 (i.e. multiplexer) of the signal acquisition unit 452. The primary switch networks 480A and 480B may be referred to as a primary multiplexer module. The primary multiplexer module can be used to switch between an EMG signal acquisition mode where EMG signals are collected and an impedance signal acquisition modes where impedance signals (i.e. skin impedance or bio-impedance) are collected.

As mentioned above, EMG signals can be acquired using a pair of electrodes to collect a differential signal. Accordingly, signal acquisition unit 452 includes a first EMG acquisition module 410A coupled to a first pair of electrodes (406A and 406B) by primary switch network 480A, and a second EMG acquisition module 410B coupled to a second pair of electrodes (406C and 406D) by primary switch network 480B. Accordingly, signal acquisition unit 452 may be used to collect EMG signals using the first electrode pair or the second electrode pair.

Signal acquisition unit 452 also includes secondary switch networks 482A and 482B. The secondary switch networks 482A and 482B may be referred to as a secondary multiplexer module. The secondary multiplexer module can be used to switch between a skin impedance acquisition mode and a bio-impedance acquisition mode, using the same set of electrodes 406.

The controller (not shown) can transmit multiplexer controller signals to the primary multiplexer module and the secondary multiplexer module to switch the signal type being sampled. The primary multiplexer module can be used to switch between acquiring an EMG signal using EMG acquisition module 410 and one of a skin impedance signal and a bio-impedance signal depending on the state of the secondary multiplexer module. Secondary multiplexer module can be used to switch between acquiring a skin impedance signal using skin impedance acquisition module 412 and a bio-impedance signal using bio-impedance acquisition module 414.

When signal acquisition unit 452 operates in a skin impedance acquisition mode, a signal can be injected using a first electrode of one of the electrode pairs (e.g. electrode 406A) and then a corresponding skin impedance signal can be received using a second electrode of the electrode pair (e.g. electrode 406B). The injected and received signals can be compared to determine the user skin impedance. When signal acquisition unit 452 operates in a bio-impedance acquisition mode, a signal can be injected using the first electrode pair and then a corresponding bio-impedance signal can be received using the second electrode pair. The injected and received signals can then be compared to determine the user bio-impedance

In some cases, the skin impedance acquisition module 412 and bio-impedance acquisition module 414 may be provided in a combined impedance module 460. The impedance module 460 may be provided as multi-channel signal injection and sensing module (as is shown in FIG. 4B). In alternate embodiments, the impedance module 460 may be a single-channel signal injection and sensing module, in which case the secondary multiplexer module may include an additional cascade of multiplexers.

In the signal acquisition unit 452, A/D converter 416 can switch between the input channels from the EMG acquisition module 410, skin impedance acquisition module 412, and bio-impedance acquisition module 414 and provide the corresponding digital signals to the controller.

In some embodiments, A/D converter 416 may have sufficient input and output channels to process multiple signals in parallel. In some cases, multiple A/D converters can be used in parallel to increase the number of channels that can be digitized at the same time or to increase the effective sampling rate.

Referring now to FIG. 4C, shown therein is a block diagram 490 illustrating components of an example multiplexer configuration that can be used in an example embodiment of a signal acquisition unit to reduce the number of input channels of the A/D converter 416. In block diagram 490, various components of the signal acquisition unit, such as the skin impedance, bio-impedance and EMG acquisition modules have been excluded for ease of understanding.

Block diagram 490 illustrates an alternate configuration of a signal acquisition unit where one or more multiplexers 492 can be used to couple a plurality of N electrodes 406 to an A/D converter having M channels, where M is less than N. This can reduce the cost of the A/D converter used to produce a wearable device such as wearable device 300.

The controller 404 and signal acquisition unit (the details of which are not shown in FIG. 4C for clarity) can be configured to oversample the electrical signals acquired by the plurality of electrodes 406 to accommodate multiplexing performed by multiplexer 492. Where a wearable device includes N electrodes 406 and the A/D converter 416 has M input channels, a sampling rate (f_(sampling)) determined using equation (1) can be used to sample the electrical signals acquired by electrodes 406 (using acquisition frequency f_(acquisition)).

$\begin{matrix} {f_{sampling} \geq {2\left( \frac{N}{M} \right)f_{acquisition}}} & (1) \end{matrix}$

For example, if an acquisition frequency of 1 kHz is specified to acquire electrical signals using four electrodes 406 (i.e. N=4), and the A/D converter 416 has a single input channel (i.e. M=1) the controller 404 and signal acquisition unit may be configured to sample the electrical signals acquired by the electrodes at eight times the acquisition frequency (i.e., 8 kHz).

Referring now to FIG. 5, shown therein is a process flow 500, illustrating various processing steps that may be performed using the described embodiments, such as wearable device 300 or system 100.

At 510, one or more raw analog electrical signal is acquired. Generally, a plurality of electrical signals will be acquired in this fashion. Each signal can be acquired using one of a plurality of electrodes such as electrodes 106, 306 and 406. In some cases, each electrical signal may be amplified before being provided to an A/D converter. In other cases, each acquired electrical signal may be provided directly to the A/D converter.

At 520, each acquired analog signal is converted to a digital signal. For example, an A/D converter such as A/D converters 316 and 416 can be used to sample and convert each analog signal to respective discrete time digital signals.

At 530, various digital signal processing techniques can be used to filter undesired components from each digital signal. For example, traditional digital signal processing techniques in either the time or frequency domain can be used to filter unwanted noise such as power line hum, motion artifacts, radio frequency etc. Examples of time domain processing techniques that may be used at 530 includes digital filters such as finite impulse response (FIR), infinite impulse response (IIR) and moving average (MA) filters.

In some cases, the acquired EMG signals may be filtered to exclude frequency content outside of a frequency range associated with EMG signals. For example, the acquired EMG signals may be filtered using a band-pass filter tuned to pass a predetermined frequency range associated with EMG signals. In some cases, the predetermined frequency range may include frequencies between 30 Hz and 180 Hz.

At 540, each processed signal can be analyzed to classify the signal and extract signal components of interest and to identify biometric features and other features of an activity being tracked. In some cases, one or more of the processed electrical signals may be combined with additional sensor signals from additional sensors such as IMU 322 and GNSS 324 for example. Analysis of the various received signals can be used to determine biometric features and other metrics for the user.

Additional signal information such as motion or position information (e.g., acquired from the IMU or GNSS unit) and other electrical signals such as skin impedance signals and bio-impedance signals can be analyzed along with the acquired EMG signals to determine biometrics and other metrics for a user. In some embodiments, data from the EMG signal and secondary signals can be assessed together. Alternatively, in some embodiments, data from the EMG signal and secondary signals can be assessed separately. Optionally, analysis of the EMG and secondary sources can be conducted concurrently or consequently. In embodiments where the analysis is conducted consequently, results from the analysis of the first parameter can inform the analysis of the second parameter.

For example, a processed EMG signal may be analyzed in conjunction with analysis of other signals such as a skin impedance signal and/or a bio-impedance signal. The skin impedance signal can be used to generate calibration data that can be used when analyzing the processed EMG signal. The calibration data may allow the analysis to account for changes in the user's physiology that are not apparent from the EMG signal alone.

Examples of biometric features may include muscle intensity, muscle coordination, muscle ratio, muscle balance, muscle fatigue, activity intensity, lactate, hydration, muscle efficiency, heart rate, respiratory rate, blood pressure, and breathing volume among others. Examples of other metrics for a user may include location, weather time, distance, calories, Vo2 max, body temperature, glucose levels, acceleration, speed, cadence, activity, pedal position, mechanical power, seat height, inclination, wind velocity, ambient temperature, humidity, air pressure, altitude among others. In some cases, the particular activity being performed by the user can also be identified based on the acquired signals being analyzed.

When multiple muscles are monitored, especially from opposite sides of the body, a comparison between electrical signals received from sensors near identical muscles (on opposite sides of the body) may be used to detect a possible muscle imbalance in one of the muscles. This can be done by comparing the temporal length and intensities of the received EMG signals for those muscles, in combination with sensor signals related to motion and/or position.

For example, to monitor muscle balance while a user is running, a pair of wearable devices 102 may be used. Each device may be positioned on the upper thigh of each user's leg with the plurality of electrodes positioned to acquire an EMG signal from the vastus lateralis (VL) muscle of the quadricep complex on both legs. The amplitude of the EMG signals may be assessed in combination with motion signals from the IMUs in each wearable device to determine whether the user's running stride is balanced. Muscle imbalance may be indicative of improper form or an impending injury. Various other features could be extracted from EMG signals to give users valuable feedback on other biometrics.

In various embodiments, the digital signal processing performed at 530 and the feature extraction and classification performed at 540 can be performed by various components of biometric tracking system 100. For example, in some embodiments, the digital signal generated at 520 may be provided directly to remote processing device 108 or a cloud server 110 without any digital processing being performed by wearable device 102.

In different embodiments, the signals may be processed at 530 by either remote processing devices 108 or cloud server 110. Similarly, the feature extraction and classification preformed at 540 can also be performed by the remote processing device 108 or the cloud server 110. In some cases, cloud server 110 may perform feature analysis in addition to feature analysis performed by a remote processing device 108, for example to identify longer term trends for a user.

In some embodiments, the controller of the wearable device 102 can perform the signal processing at 530. In some cases, the wearable device 102 can then provide the processed signal data to a remote processing device 108 or cloud server 110. In other cases, the controller may also perform some or all of the feature extraction and classification at 540. In embodiments where multiple wearable devices are used to assess biometrics or other metrics, one or more of the multiple wearable devices may perform the signal processing, including feature extraction and classification.

At 550, the biometric features and other metrics identified at 540 can be stored or provided to a user as feedback. In various embodiments the features identified at 540 may be stored in memory module 318 on wearable device 300, in a memory module of remote processing devices 108, in a cloud storage module of cloud server 110, or in a combination of these storage locations.

In some cases, the wearable device or a remote processing device (e.g., a mobile phone) may include a display. The wearable device or remote processing device can be configured to display feedback based on the at least one biometric identified at 540. For example, the feedback provided to a user may be a report or a visualization of the at least one biometric.

In some cases, the remote processing device or wearable device may include a user interface for changing or adjusting the display being provided. For example, the display may include different reports or visualizations, and a user may be able to scroll or browse through the different feedback available. In some cases, the configuration of the feedback on the display can also be customized based on a user's preferences.

In some cases, the display on the remote processing device or wearable device can be placed into a sleep mode to reduce battery consumption. The display may be activated based on input received from a user. In some cases, the display can be automatically activated where the processing performed by the wearable device, remote processing device or cloud server generates an alert for the user, such as an indication of fatigue, dehydration, or potential injury.

The display may also provide summary information to a user regarding a completed activity. In some cases, historical records stored on a remote processing device or cloud server can be displayed to a user to illustrate progress trends in the user's activity and physiological response.

Referring now to FIG. 6, shown therein is a flowchart illustrating an example embodiment of a method 600 for biometric tracking. Method 600 can be performed using components of system 100 and wearable devices 102 and 300.

At 610, a plurality of electrical signals, including at least one EMG signal, are captured using the electrodes on the wearable device. The signals can be digitized by an A/D converter of the signal acquisition unit and provided to the controller on the wearable device. As mentioned above, in some cases the signals may be amplified prior to being digitized. As well, the signals may be provided to the controller unfiltered such that all filtering of the acquired signals is performed after digitization.

In some cases, the plurality of electrical signals can include skin impedance signals or bio-impedance signals. In some cases, skin impedance signals can be acquired using two electrodes positioned on the user's skin surface. For example, a small current signal can be injected into the user's skin surface using a first electrode of an electrode pair (e.g. electrode 406A) and received by a second electrode of the electrode pair (e.g. electrode 406B). In some cases, the electrodes in the electrode pair can be positioned nearby (e.g. within ˜1 cm) to one another to maximize the conduction that occurs through the user's skin. The amplitude of the signal received by the second electrode may be compared to the amplitude of the injected signal to calculate the impedance of the user skin surface. The phase of the received signal may also be compared across differing frequencies.

Bio-impedance signals can be acquired by measuring signals using a tetrapolar electrode configuration. A signal can be injected into the user's body using a first electrode pair (e.g. 406A and 406B). The signal received by a second electrode pair (e.g. 406C and 406D) can be measured. A comparison of the injected signal to the received signal can be used to determine bio-impedance for the user.

In some cases, the electrode pairs can be positioned at far apart locations on the user skin surface, such as cross-body or at opposite ends of a limb such that skin conduction in negligible. This may also provide an indication of the user's bio-impedance that is more representative of the hydration levels throughout the user's body, rather than in a localized region. In some cases, the electrodes may be placed on the same limb, such as a first electrode pair on the front of a user's thigh and a second electrode pair on the back of the user's thigh.

To acquire both the bio-impedance signal and the skin impedance signal, a similar process can be used. In each case, an AC injection signal can be generated, e.g. a 50 kHz signal. The injection signal can be current limited (e.g. less than 1 mA) to prevent a build-up of capacitance. A multiplexer configuration, such as the configuration described above with reference to FIG. 4B, can be used to route the injection signal to a first electrode (in the case of skin impedance sensing) or to a first electrode pair (in the case of bio-impedance sensing).

The impedance signal received by the second electrode (or electrode pair) can be provided as an input to a differential amplifier. As well, the injected signal can be tapped to the differential amplifier. The output of the differential amplifier can be fed into a full wave rectifier module which removes the AC component of the differential amplifier output signal to obtain a root mean square (RMS) value of the output signal. The RMS value can be passed through a low pass filter to obtain a DC voltage level. The DC voltage level can be used to determine the magnitude of the impedance signal.

In other cases, an inphase/quadrature (I/O) demodulator can be used to determine impedance. An injection signal can be generated and injected to the user skin surface using a first electrode (for skin impedance) or first pair of electrodes (for bio-impedance) as described above. An impedance signal can then be acquired using a second electrode (skin impedance signal) or second pair of electrodes (bio-impedance signal) as described above. The impedance signal can be provided to a differential amplifier, and the differential amplifier output signal can be provided to the inphase/quadrature demodulator. The in-phase and quadrature components of the voltage can then be extracted from the amplified voltage signal.

An oscillator can be used to demodulate the amplified voltage signal. The oscillator source signal can be configured to correspond to the generated injection signal. That is, the oscillator in-phase signal can have the same frequency and phase as the injected signal. An oscillator quadrature phase signal can then be generated by delaying the in-phase signal by 90°. The in-phase and quadrature phase oscillator signals can be switched and fed to a mixer.

The mixer can combine the in-phase and quadrature phase oscillator signals with the amplified voltage signal to generate in-phase and quadrature phase voltage signals respectively. Each of the in-phase voltage signal and the quadrature voltage signal can be passed through a low pass filter to obtain DC values for the in-phase and quadrature signals. These signals can then be used to determine the real and imaginary components of the impedance.

At 620, calibration data is generated based on a subset of the electrical signals acquired at 610. For example, the plurality of electrical signals acquired at 610 may include one or more skin impedance signals and/or one or more bio-impedance signals. The calibration data can be generated based on acquired skin impedance signals to account for changes in the EMG signal that may be caused by changes in the conductivity of the user's skin surface. As described above, in different embodiments the calibration data may be determined by any one or more of the wearable device, remote processing device or cloud.

At 630, the calibration data is used to process the EMG signal using the calibration data. As mentioned, the calibration data may account for changes in conductivity of the skin surface that affect the EMG signals acquired at 610.

At 640, at least one biometric is determined from the processed EMG signal. For example, the biometric may be one or more of muscle intensity, muscle coordination, muscle ratio and muscle fatigue for targeted muscles. In some cases the biometrics may be determined from analyzing the EMG signal in combination with additional sensor information such as motion data or bio-impedance data for example.

Once the at least one biometric has been determined at 640, additional biometrics and other metrics may also be determined in a similar manner as described in methods 500 and 600. The at least one biometric may then be stored or displayed as described above at 550 of method 500.

Referring now to FIG. 7, shown therein is a diagram illustrating various components of system 700 that can be used to acquire and process electrical bio-signals.

Generally, system 700 includes a wearable device that is generally analogous to wearable devices 200 and 300, and which includes a plurality of electrodes 706 a-706 n positioned to acquire an electrical signal from a user skin surface when the wearable device is secured to the user skin surface. The electrodes 706 are coupled to a signal acquisition unit 702 and a signal injection unit 762. Signal acquisition unit 702 may correspond generally to the signal acquisition unit described herein with reference to FIGS. 3 and 4.

The system 700 may also include a processing module 790. The various components of processing module 790 can be distributed between a wearable device, remote processing device and cloud server in different embodiments. Processing module 790 includes a calibration unit 750, a feature processing module 740, one or more communication module 770, one or more storage modules 780 and a signal injection controller 760.

Signal acquisition unit 702 is operatively coupled to the calibration unit 750 and the feature processing module 740. Feature processing module 740 includes a pre-processing unit 742 and a feature identification module 744. Signal acquisition unit 702 may acquire electrical signals using the electrodes 706 and digitize the acquired signals as described herein. These signals may then be provided to the calibration unit 750 and/or the feature processing module 740 for further processing.

In some embodiments, one or both of the feature processing module 740 and the calibration unit 750 may be provided on the wearable device itself. In other embodiments, the feature processing module 740 and the calibration unit 750 may be located on a remote processing device or cloud server, and the digitized signals may be communicated without any processing from the wearable device to the feature processing module 740 and calibration unit 750 using one of the communication modules 770. In some cases, aspects of the feature processing module 740 and the calibration unit can be distributed among the wearable device, remote processing device and cloud server.

For example, signal acquisition unit 702 may acquire digitized skin impedance signals provide these to the calibration unit 750. The calibration unit 750 may generate or update calibration data based on the received signals. The calibration data can then be provided to the feature processing module 740 for use in processing the acquired signals and identifying various biometrics from the acquired signals. In some cases, the calibration unit 750 may also use pre-processing unit 742 to pre-process the received signals to remove noise and other undesired signal components before generating the calibration data.

Generally, the pre-processing unit 742 can be used to remove undesirable signal components from the received digital signals. In some embodiments, the pre-processing unit 742 may also be used to calibrate the received digital signals using the calibration data generated by the calibration unit 750.

The feature identification module 744 can be used to analyze the received electrical signals (and other sensor signals) to identify at least one biometric for the user. In some cases, the feature identification module 744 can be used to determine a plurality of biometrics and other metrics for the user. The feature identification module 744 may also be used to analyze trends and provide feedback and alerts to a user based on the analysis.

Skin conditions, such as perspiration, and other constantly changing environmental factors can impact the strength and other properties of the EMG signals. Calibration data can thus be used to enable reliable comparison between EMG signals acquired throughout the performance of an activity, and over time as these parameters change.

Signal injection controller 760 may be used to generate and provide precursor signals used in acquiring a skin impedance signal and/or a bio-impedance signal. Signal injection controller 760 may inject small electrical pulses into particular electrodes 706 using signal injection unit 762. The corresponding electrical signals received at other electrodes 706 can be analyzed to determine features such as skin impedance and bio-impedance, as discussed above.

For example, the relative amplitude of the received signals can be compared with the amplitude of the injected signals. This can be used to generate calibration data, which can in turn be used to process the EMG signals and determine various biometrics. For example, hydration may be determined by analyzing a bio-impedance signal acquired from an injected electrical pulse. Hydration may be determined in various ways, such as using existing hydration vs. bio-impedance models, lookup tables, or trained machine learning models.

Signal injection controller 760 may also be used to detect when one or more electrodes 706 have become disconnected or are not in contact with a user skin surface. By detecting an open circuit in an electrode 706, system 700 may determine that the electrode has lost contact either with the user skin surface, or has become disconnected from the wearable device. Accordingly, an alert may be provided to the user indicating that the lead has been disconnected.

While the applicant's teachings described herein are in conjunction with various embodiments for illustrative purposes, it is not intended that the applicant's teachings be limited to such embodiments. On the contrary, the applicant's teachings described and illustrated herein encompass various alternatives, modifications, and equivalents, without generally departing from the embodiments described herein. 

The invention claimed is:
 1. A biometric analysis system comprising: a remote processing device; and a wearable device, the wearable device removeably securable to a user skin surface with a skin-facing surface of the wearable device positioned to make contact with the skin surface, the wearable device having: a plurality of electrodes positioned to acquire an electrical signal from the skin surface; a controller; a signal acquisition unit operatively coupled to the controller and to the plurality of electrodes, the signal acquisition unit having a skin impedance acquisition module and an electromyography acquisition module; and a wireless communication module operatively coupled to the controller to communicate with the remote processing device; and at least one of the controller and the remote processing device is configured to: cause the injection of at least one precursor signal into at least one of the plurality of electrodes; capture, via the signal acquisition unit and the plurality of electrodes, a plurality of electrical signals comprising at least one electromyography signal and at least one impedance signal based on the at least one precursor signal; generate calibration data based on the at least one impedance signal; and process the at least one electromyography signal using the calibration data to determine at least one biometric.
 2. The system of claim 1, wherein: the at least one impedance signal comprises at least one skin impedance signal; and the subset of the plurality of electrical signals used to generate the calibration data comprises the at least one skin impedance signal.
 3. The system of claim 1, wherein the at least one biometric comprises at least one of muscle intensity, muscle coordination, muscle ratio, and fatigue.
 4. The system of claim 1, wherein the wearable device further comprises at least one of an inertial measurement unit and a GNSS unit.
 5. The system of claim 1, wherein each electrode is a passive electrode.
 6. The system of claim 5, wherein the signal acquisition unit further comprises a bio-impedance acquisition module.
 7. The system of claim 6, wherein the signal acquisition unit further comprises: a primary multiplexer module; and the signal acquisition unit is coupled to the plurality of electrodes using the primary multiplexer module.
 8. The system of claim 7, wherein the signal acquisition unit further comprises: the primary multiplexer module coupled to the plurality of electrodes; and a secondary multiplexer module coupled to the primary multiplexer module; wherein each of the skin impedance acquisition module and the bio-impedance acquisition module is coupled to the primary multiplexer module by the secondary multiplexer module; and the electromyography acquisition module is coupled directly to the primary multiplexer module.
 9. The system of claim 5, wherein the wearable device further comprises: an analog to digital converter coupled to the controller; and each of the skin impedance acquisition module, the bio-impedance acquisition module, and the electromyography acquisition module are coupled to the controller by the analog to digital converter.
 10. The system of claim 9, wherein each of the skin impedance acquisition module, the bio-impedance acquisition module, and the electromyography acquisition module provide unprocessed signals to the analog to digital converter.
 11. The system of claim 10, wherein the electromyography acquisition module has an amplifier that amplifies the electromyography signal prior to providing the electromyography signal to the analog to digital converter.
 12. The system of claim 1, wherein the remote processing device is a mobile device.
 13. The system of claim 1, wherein the remote processing device comprises a display, and the remote processing device is configured to display feedback based on the at least one biometric.
 14. The system of claim 13, wherein the feedback comprises at least one of a report on the at least one biometric and a visualization of the at least one biometric.
 15. The system of claim 1, further comprising: a cloud server having a cloud storage module that stores a user profile associated with the wearable device, wherein the user profile includes a historical record of the at least one biometric.
 16. The system of claim 15, further comprising: a plurality of wearable devices; and wherein the cloud storage module stores a unique user profile for each user in a plurality of users, and each wearable device is associated with one of the unique user profiles.
 17. The system of claim 1, wherein the wearable device further comprises an alignment guide for aligning the wearable device with a desired region of the skin surface.
 18. The system of claim 1, wherein each electrode is an active electrode.
 19. The system of claim 1, wherein: the at least one impedance signal comprises at least one bio-impedance signal; and the subset of the plurality of electrical signals used to generate the calibration data comprises the at least one bio-impedance signal.
 20. A wearable device for biometric analysis, the device comprising: a skin-facing surface removeably securable to a user skin surface, with the skin-facing surface positioned to make contact with the skin surface; a plurality of electrodes positioned to acquire an electrical signal from the skin surface; a controller; and a signal acquisition unit operatively coupled to the controller and to the plurality of electrodes, the signal acquisition unit having a skin impedance acquisition module and an electromyography acquisition module; the controller configured to: cause the injection of at least one precursor signal into at least one of the plurality of electrodes; capture, via the signal acquisition unit and the plurality of electrodes, a plurality of electrical signals comprising at least one electromyography signal and at least one impedance signal based on the at least one precursor signal; generate calibration data based on the at least one impedance signal; and process the at least one electromyography signal using the calibration data to determine at least one biometric.
 21. A method for biometric analysis using a wearable device positioned to make contact with a skin surface of a user, the wearable device having a plurality of electrodes positioned to acquire an electrical signal from the skin surface, the method comprising: causing the injection of at least one precursor signal into at least one of the plurality of electrodes; capturing, via the signal acquisition unit and the plurality of electrodes, a plurality of electrical signals comprising at least one electromyography signal and at least one impedance signal based on the at least one precursor signal; generating calibration data based on the at least one impedance signal; and processing the at least one electromyography signal using the calibration data to determine at least one biometric. 